The present application claims priority of German application No. 10039482.5 filed Aug. 8, 2000.
Not Applicable
The invention relates to a handler for transporting planar substrates, in particular wafers, used in the semiconductor industry.
In semiconductor production it is known that every contact between a wafer and a bearing surface, for example in a storage cassette or during transport between work stations on the support arm of a wafer handler, can generate particles which can adversely affect the production yield.
Moreover, it has been found that areas of a wafer which have come into contact with a bearing surface no longer have a sufficient surface quality for them to be used in a conventional production process which includes photolithographic steps.
U.S. Pat. No. 5,810,155 discloses an object-transporting device which uses acoustic levitation. This object-transporting device comprises a transport track for this purpose. The transport track is set in vibration on one side by an ultrasound generator, and an absorber is provided at another point on the transport track. In this way, a migrating bending wave develops on the transport track by means of which an object lying thereon can be transferred along the transport track with the wave. Said patent specification thus follows another principle and is therefore not relevant to the present invention.
The underlying principle of acoustic levitation on a flexural vibrator set in vibration by a vibration generator is described in the publication xe2x80x9cThe Journal of the Acoustical Society of Americaxe2x80x9d, Vol. 100, No. 4, part 1, October 1996, Hashimoto et al.: xe2x80x9cNear-field acoustic levitation of planar specimens using flexural vibrationxe2x80x9d. However, said publication does not contain any reference to integrating such a flexural vibrator in a concrete handler for planar substrates.
It would therefore be desirable to provide a handler, in particular for wafers, which would largely avoid the abovementioned problems.
A handler is disclosed for transporting planar substrates, in particular wafers, used in the semiconductor industry, between at least two stations. The handler comprises a movable flat support arm for receiving a substrate and means for maintaining the substrate in a predetermined position on the support arm. A vibration generator is provided for generating a longitudinal ultrasonic vibration. The vibration generator interacts with the support arm in such a way that a substantially stationary vibration with at least one antinode can be generated on the flat support arm. This permits a levitation of a substrate placed thereon. The means for defining the location of the substrate provide lateral positioning exclusively by an interaction with the edge area, preferably the rim of the substrate. By this procedure, a substrate can be taken up from one work station by means of the support arm, without any appreciable contact being made with the underside, transported to another work station by movement of the support arm, and deposited there, likewise without any appreciable contact being made with the underside of the substrate. In this way, not only is it possible to avoid unnecessary particle generation caused by an interaction of the support arm with a bearing surface, but the underside of a substrate can be used without any loss of quality in, for example, a photolithographic production step. This procedure is based on the knowledge that, when a support arm interacts with a vibration generator, the support arm represents a flexural vibrator in which a near-field levitation is used to lift a substrate when a substantially stationary vibration develops on the flexural vibrator.
The means for lateral positioning of the substrate prevent a xe2x80x9cdriftingxe2x80x9d of the levitated substrate on the support arm. For this purpose, the means for lateral positioning act very specifically on only the edge area of a substrate, preferably only on the outer rim of a substrate in the case of tactile positioning, in order to avoid an undesired interaction with, in particular, inner areas of the underside of the substrate.
Near-field levitation develops in a favorable manner in particular when the vibration generator interacts with the support arm in such a way that a substantially stationary vibration with a multiplicity of vibration nodes is set on the flat support arm.
In addition, it is particularly advantageous if the vibration generator is arranged on the support arm in such a way that the longitudinal vibration axis is oriented perpendicular to the plane of the flat support arm. In this way the energy of the vibration generator can be transmitted particularly effectively to the support arm.
In a preferred embodiment of the invention, the support arm is configured in such a way that a received substrate is accessible from underneath in the area of a predetermined lateral position, for example, a transport position. This can be achieved by means of openings made in the support arm or by an appropriate shape, for example, a fork or tongue shape or the like. These shapes are based on the knowledge that levitation of a component on a support arm designed in this way functions free of problems, even though the bearing surface for the substrate is smaller than the substrate surface. Finally, this affords the advantage that the substrate can be easily taken up and then deposited again.
In a preferred embodiment of the invention, the means for lateral positioning of a substrate can comprise one or more suction heads which act on the edge area of the substrate. In this way the substrate comes into only minimal contact on the suction points of the suction heads at the edge.
In one embodiment of the invention, the substrate is laterally centered in the desired position by at least one limit stop which acts on the edge area of a substrate. The positioning with one or more limit stops can also take place in combination with suction heads which, by means of their suction action, draw the substrate toward the limit stops. In another embodiment of the invention, the means for providing lateral positioning comprises a clamp device. The clamp device can hold an edge area of the substrate in as it were the manner of forceps.
Lateral positioning of a substrate in the desired position can also be achieved by means of the support arm being tilted away from the horizontal, that is to say inclined. This embodiment is advantageous in particular in combination with suitably arranged limit stops. In a further embodiment of the invention, devices are provided which permit completely contactless lateral positioning of a substrate. The substrate can thus be xe2x80x9chandledxe2x80x9d in a completely contactless manner, by which means particle generation or surface contamination because of contacts can be completely avoided. A contactless positioning can be achieved by a reflector arranged laterally on the substrate or by several such reflectors which preferably do not communicate with the support area of the support arm.
Moreover, at least one additional vibration generator can be used in the area of the substrate for contactless lateral positioning, which additional vibration generator preferably does not communicate with the support area of the support arm.
Likewise, one or more nozzles through which gas or air flows can be used for contactless positioning.
Depending on the intended use, a plurality of support arms can be arranged either alongside one another and/or above one another and/or opposite one another. These support arms can be fed from one or more vibration generators for developing a flexural vibration, it being possible for the one vibration generator or the several vibration generators to be arranged on and/or under the support arms.